Unstaffed petrol stations are helping drive lower fuel prices in their local areas, according to the Commerce Commission.
Its analysis showed areas that included at least one unstaffed fuel station within a five-minute drive, had prices that were on average six cents per litre lower than those without unstaffed stations.
However, the competition watchdog said self-serve stations run by supermarkets did not have the same effect.
"Our findings reinforce that unstaffed stations are definitely the way to go for cheaper fuel and anyone who has had one open in their area has probably experienced lower prices," commissioner Bryan Chapple said.
He said local councils should think about the competition benefits of self-serve fuel stations when planning and considering consent applications.
"New Zealanders spend around $10 billion at the fuel pump every year, so even a small reduction in prices can put money back into the pockets of Kiwis," Chapple said.
"This pricing pressure - and motorists choosing to shop wisely - also creates an incentive for staffed sites in the local area to reduce their prices."
The commission said the analysis followed a "please explain" letter it issued to fuel companies last year, asking for information on "anomalies" in the market.
"As well as reviewing the information the fuel companies provided us, we have used data from fuel pricing app, Gaspy, to assess the effect on local fuel prices when an unstaffed petrol site opens - which is greater competitive pressure," Chapple said.